Nanowires spot DNA mutation

Harvard University researchers have demonstrated
that it is possible to detect sequences of DNA that cause cystic fibrosis
in real-time using a sensor made from nanowires.

Nanowire sensors could eventually be built into labs-on-a-chip
that could be used for medical diagnostics and pathogen detection in the
field, and for drug discovery.

The researchers' method is sensitive, and can be optimized to
be even more sensitive, according to the researchers. The prototype detected
a DNA sequence in a small drop of solution that contained as few as 1,000
DNA molecules. The device could prove sensitive enough to work in the
field to detect DNA sequences without the common step of amplifying, or
replicating, the DNA until there is enough to test. This would make for
faster, less expensive DNA testing.

DNA is formed from four types of bases connected to a sugar-phosphate
backbone. The researchers' device consists of a set of 20-nanometer-wide
silicon nanowires that have surface layers of peptide nucleic acid receptors
designed to recognize the mutation -- three missing bases -- that causes
75 percent of cystic fibrosis cases.

Each nanowire is connected to electrodes at either end, and the
device is positioned inside a microfluidic channel that flows the sample
across the sensor. When target DNA molecules bind to the peptide receptors,
the electrical conductance of the nanowires increases, signaling the DNA's
presence.

Nanowire sensors could be used in practical applications in two
to five years, according to the researchers. The work appeared in the
January 14, 2003 issue of Nano Letters.